The anomeric specificity of beta-galactosidase and lac permease from Escherichia coli.
Beta-Galactosidase was found to act on alpha-lactose slightly more than twice as rapidly as on beta-lactose for both the hydrolysis and transgalactosylis reactions. The effect was shown to be on the Vmax values; the Km values for the different anomeric forms were the same. The step of the reaction for which the enzyme has anomeric specificity was shown to be glycosidic bond breakage. The steps in glucose release or in the glucose acceptor reaction were not affected by anomeric composition. Neither allolactose hydrolysis nor transport of lactose into the cells by lac permease was sensitive to the anomeric composition of the substrate. The implications of these results for lac operon induction and for lactose metabolism are discussed.
D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D005696:Galactosidases / Q000378:metabolism*; D005947:Glucose; D007700:Kinetics; D007785:Lactose; D026901:Membrane Transport Proteins / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins; D009598:Nitrophenylgalactosides; D013237:Stereoisomerism; D013379:Substrate Specificity; D027981:Symporters; D001616:beta-Galactosidase / Q000378:metabolism*
D029968:Escherichia coli Proteins; C050221:LacY protein, E coli; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D027981:Symporters; D009598:Nitrophenylgalactosides; C001970:allolactose; C021499:lactose permease; D005696:Galactosidases; D001616:beta-Galactosidase; D005947:Glucose; D007785:Lactose